(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of preventing the arcing effect during contact implant by using a conductive shield within the contact opening in the fabrication of integrated circuits.
(2) Description of the Prior Art
In the manufacture of semiconductor devices, it is necessary in many processes to perform an ion implantation within a contact opening. For example, this may be used in fabricating CMOS logic circuits. During contact implantation, the wafer must be held within the implantation chamber. Usually, a mechanical chuck holds the wafer in place. Particle contamination and implant shadowing at the edge of the wafer have been found to be disadvantages of a mechanical chuck. To avoid these damages, an electrostatic chuck has been used to increase the useful wafer area, eliminate implant shadowing, and reduce particle contamination. To maintain enough holding force, a six-phase AC square wave with 1000 volts is applied on six sectors so that at least four sectors are kept at full voltage.
A ring-type electrostatic discharge defect has been observed after contact implantation. This defect has been found to be attributable to the electrostatic chuck used to hold the wafer during contact implantation. The yield loss is about 40% due to this defect. It has been determined that the damage is due to the non-uniformly distributed electric field around the wafer which causes an non-uniformly distributed charge accumulation on the photoresist surface leading to the electrostatic discharge damage, or the so-called arcing effect. The electrostatic discharge damage can be eliminated by replacing the electrostatic chuck with a mechanical chuck. However, the cost is a loss of the advantages of the electrostatic chuck. It is desired to find a way to prevent electrostatic discharge damage while using an electrostatic chuck to hold a wafer during contact implantation.
U.S. Pat. No. 5,665,629 to Chen et al teaches forming a high resistance film such as SiN, SiO.sub.2, or TiO.sub.2 within a contact opening and then filling the opening with a metal plug. Ti/TiN has often been used in the art as a barrier layer under a metal plug, such as in U.S. Pat. No. 5,654,234 to Shih et al, for example. Titanium has also been used as a silicide layer over gate electrodes and source/drain regions, such as in U.S. Pat. No. 5,723,893 to Yu et al, for example.